Method for removing scale



Patented June 5, 1951 UNITED STATES PATENT OFFICE 2,556,128 METHOD FonREMoVlNG SCALE Thomas L. B. Webb, Los Angeles, Calif.

Application August 17, 1945, Serial No. 611,131

This invention relates to a method for removing water scale, or thedeposits from water in water handling equipment. I have discovered thathydrogen zeolite water may be effectively employed for removing depositsmade in water handling equipment yand which form scale or coatingstherein.

I have further discovered that such hydrogen zeolite treatment of suchequipment or apparatus can be effected without danger of the saidtreated water attacking the equipment.

In the utilization of water tube boilers, steam superheaters, waterheaters, heat exchangers, pressure vessels, and other similar equipmenthandling water, it is common for such equipment to become scaled orcoated with chemical deposits from the water. Such chemical depositsusually include carbonates of sodium, calcium, magnesium, and the like.When the equipment becomes scaled, the heat exchange efficiency of suchequipment is greatly reduced substantially in proportion with the amountof scale deposited in the equipment. As the scale builds up to Where theheat exchange from the exterior of the equipment to the water within theequip ment is materially reduced, it is very possible for the equipmentto burn out.

It is therefore an object of this invention to provide a method ofremoving scale deposited by water from within water handling equipmentsuch as superheaters, boilers, heat exchangers, vessels and the like,which includes the treatment of the scale surface of such equipment withhydrogen zeolite water.

Another object of this invention is to provide a method for the removalof such scale deposits as sodium, calcium and magnesium carbonates andother scale deposits from the surfaces upon which they are deposited bythe treatment of the said surfaces with hydrogen zeolite water wherebythe hydrogen ions of the hydrogen zeolite water act to replace thesodium, calcium and magnesium ions of the scale.

Another object of this invention is to provide i a method for theremoval o1 scale from water carrying equipment which includes the stepsof treating the scale with hydrogen `zeolite water, determining the pHof the hydrogen zeolite water, and continuing the treatment until the pHremains substantially constant and then washing the equipment.

Other objects and advantages of this invention it is believed will beapparent from the following detailed description ci a preferredembodiment thereof as illustrated in the accompanying drawing,

5 Claims. (Cl. 134-22) T he drawings constitute a diagrammaticillustration of the apparatus used in carrying out my process andembodying my invention.

In accordance with the preferred embodiment of my invention the methodas it is herein illustrated is shown and explained in conjunction twiththe removal of water deposited scale or coat-l ing from within the coilsof a steam superheater, although my invention is in no way limited inits applicability to the treatment of such scaled tubing.

In this embodiment of my invention the superheater as shown for thepurpose of illustration includes a nre box l which may constitute theframe work of a furnace or may be of any other suitable or desirableconstruction.

Supported Within this frame work is a series coil 2 in which water orsteam which it is desired to superheat is circulated from an inlet 3 toan outlet 4. In this modification the superheating is carried out bymeans of heated gases which flow over the tubes through the re box inthe direction substantially as indicated by the arrows 5. The gases aredrawn away from the tubes usually by means of a fan 6 and may bedischarged at any suitable point. The rate of withdrawal of these gasesmay be controlled by means of a damper l and of course by speed ofoperation of the fan 6.

In the use of such :a superheater there is a tendency of the scale toaccumulate in the lower bends `8 due somewhat to the contractions andexpansion of thetube sections above the bends 8 which results inloosening of the scale at the points above the bends 8 and permittingthe same to fall to the lowermost bends. It has proven particularlydifcult to remove the scale from tubes 0f this character and ordinarymethods have been found inadequate. The most practical method heretoforeollowed has been to dissolve the Scale by circulating ordinary waterthrough the `coils for a long period of time su-l cient to enable thematerials of the scale to be dissolved in the water. This requires thehandling of extremely large quantities of water and a long period oftime because the solubility of the materials making upthe scale is verylow in ordinary water. It has been found impractical to try to utilizeacid methods of treatment in the removal of the scale from such scaleencrusted tubes because of the fact that such. treat` ments result inthe acid so attacking the tubes as to very materially shorten theirlives, not only during the treatment, but after the treatmentA hasdiscontinued due to the accumulation of the acid within the bends 8.

It is impractical to try to Vaporize the water containing the acid inthe bends 8 because the addition of heat to the coils containing theacid results in very rapid chemical reaction between the acid and theiron or steel making up the coils with their subsequent failure.

In carrying out my invention I employ an ordinary commercial form ofhydrogen zeolite generating ,apparatus diagrarnmatically illustrated at9. The generator `9 is a steel tank having a protective lining (notshown) and containing a commercially available acid-resistant zeolite.The generator operates on the principleofionexchange. The mineral saltspresent in the raw water supply are practically completely-disassociated into ions. The principal ionspresent are the cations ofcalcium, magnesium and sodium and the anions of bicarbonate, :sulphateand chloride. Raw water is passed through inlet :I3 :into .the:generator `.-9 and v.downwardly -gthroughthe bed -ofzeolite (notshown). As the water flows,down through the unit the `zeolit-e,-ggranulestake out kthe cations of caicium, magnesiumcand `sodiumandygive up Vhydrogen ions .inexchangeto iormacids The carbonio 'acidformed v.from the bicarbonates breaks down-immediatelydnto carbondioxide and water. -Sulphuric and rhydrochloric acids are formed from:the sulphate and .chloride ions. The ywater s.

treated is circulated as described below. The ,generating uniti). isconnected. through a'- suitable Iflexible connection lwith Vthe inlet -3of thecoil. .Theoutlet.,4.of.the coil may be connected with .anysuitablewaste orother point of -disposal of the Water, or may be connected'tothe inlet 1.3 vf theunit9 Aas `shown in the drawings. Connected-inrtheiiexible conduit lis :a three-Way valve, .theJoranch l l of which is"connectedwith .,.theoutlet branch fof the hydrogenzeolite vunitvbanditi-ie:inlet branch vi2 of whichis connected NVwithan ordinary-sourceof Water. In thisvman- Anerztlfiehydrogen-zeolite water from thetreating .unit Smay .be circulated-through the coil Y2'until -all-of thescale within the coil has been-removed. A'Ihisfremoval Iof the-scale is-by :hydrogenion re- :placement of the-sodium, calcium-and magnesiumyions-which usually are combined With carbon dioxide, sulphate,chloride, or similar radicals, to .form .the substantially insolubleprecipitate of `which .thegscalegis composed. The Yhydrogen .iongeplacementresults in the vrformation of theaoids.with-either-thefcarbon dioxide, sulphate,` chloride, or.other.radicals,Awhich then pass .into the 'so v.lution. The sodium, calcium and`magnesium valso .passlinto solution with a reduction of the hydrogenfion concentration, and these `base radi- :cals vbecome embedded uponthe zeolite in the hydrogenzeolite generating unit when the outlet .f4.of v,thecoil is connected to the .inlet i3 of thehydrogen `zeoliteunit. This process-oi circulating thehydrogen .zeolite water through.the vzeolite in .the unit i9 iis .continued luntil analysis of .the.return Water f shows substantial :constancy of the pI-I value thereof,,indicating that the Water `upon continued circulation -is notdissolving or rremoving,further scale vfrom the coil 2. This indicatesthat the scale has `been substantially completelyA removed.

This reaction not only .removes the sodium, calcium randmagnesiumdeposits, but also results in the removal lof Ythe silica depositsywhich may makeup a .considerable portion of the scale.

As `an `example of the foregoing, ,in a superk heater similar to thatshown in .the accompanying drawing, hydrogen zeolite Water' Wits. Qi

culated through the inlet 3 having an initial pH of 4.4 and the rsthydrogen zeolite Water passed out of the outlet 4 showed a pick-up of17,000 parts per million of solids with a resulting pH of 10.7. Thecirculation was continued for a period of approximately 60 hours, whenit was observed that the pH of the water leaving the outlet 0 was 4.4,indicating no further action. The inn iow-f of hydrogen` zeolite watervwas stopped.

A three-way valve in the'exible conduit l0 is rotated to a position toadmit ordinary supply Water into the inlet 3 to wash out the hydrogenzeolitelwater. The water flow was then stopped and the coils were blownout with air. The susperheate'r =was1then returned to service.

.Before this .operation of removing the scale was performed, it wasdetermined that there was a.'-'scaleo'f approximately 1% inch thicknessupon the inner surface of the coil 2.

This superheater in service before the washing -operation '-showedanfexcess in temperature .of A.about-35" in the 'tubes due totheoverheating of these tubes'because of the insulating eiect :of .the:scale within `the interior of the tubes. Upon `completion of thedescaling operation, the excess temperatures were entirely eliminatedandit -was found that the Aoperating tube temperatures were on :an averagelower than -when the unit was first placedin service, indicating notonly the removal lof .the scale deposited `byltlie water, -butalso'indicating-the removal of some ofthe vmill scale which undoubtedlyexisted in 'the tubes upon their original installation.

After continuedrecirculation ofthe water-freni lsuch adescalingloperation into the hydrogen. 4ze'oliteunit,zit isnecessary, toregeneratethe hy`- vdrogen zeolite unit by .the use of a quantity ciVthe vacid(sulphuricI-IZSOi) las is Well understood inthe Tartes@ thatthe unit may again be placed .in .operation Dilute rsulphuric acid ispassed through the bed of zeolites to remove therefrom the f-ionsabsorbed from the Water. The bed .is then .washed'with water to removeexcess `acid` andis -thenready for a resump'tion'of the'cycie,

:Having-.fully described my inventionit is to .be understood that I doinot Wish to be `liiiiitei Vto the-details herein set'forth,but'myinvent'ion isro'f the'full scope of-the appended claims.

I claim:

31. The method of removing water 'deposited scale'from the surface of awater container-which includesthe steps of removing the scale from'thesurface by passing hydrogen 'zeolite water over the surface, the waterhaving an acid vand continuing the treatment until the pH of the Waterafter passing over the surface remains substantiallyconstant and untilthe pH of the Water after-passing over the surface becomessubstantiall-y equal -to therpH of the hydrogen zeolite Water before itis passed over the surface of the container.

'2. The method of cleaning a water container of water deposited scalewhich includes the steps of passing hydrogen zeolite wat-er having anacid pH through the water container until the pH o the inlet Water andpI-I of the outlet water the'systemare substantially the same.

3. The method of removing Water deposited scale from the coils of asuperheater which in-` cludes the -steps of circulating hydrogen zeolitewaterfhaving an acid vpH through the coils, determining 'the initial pHof the hydrogen Zeolitev Water, .and continuing the circulation untilthe pH of the water at the discharge iromithe coils 5 is substantiallyequal to the pH of the water at the inlet of said coil.

4. The method of removing water deposited scale from the coils of asuperheater which includes the steps of circulating hydrogen zeoliteWater having an acid pHI through the coils, the hydrogen zeolite waterbeing of initially determined jacid pH, and continuing the circulationuntil the water at the discharge from the coils substantially the sameas the pH of the water a: n

the inlet of said coil, and then washing out tht, coils'.

5. The method of removing water deposited scale from the heating coilsof a superheater which includes the steps of circulating hydrogenzeolite Ywater through the coils until the hy` drogenfzeolite water nolonger picks up scale 6 material from the coils the acid pH of thehydrogen zeolite Water entering the coils being substantially the sameas the acid pH of the Watei leaving the coils.

THOMAS L. B. WEBB.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,089,317 Wilder Aug. 10, 19372,233,852 Schmitt Mar. 4, 1941 15 2,294,765 Urbain Sept. l, 194:22,295,204 Dockray Sept. 8, 1942 2,325,675 Gustafson Aug. 3, 1943

1. THE METHOD OF REMOVING WATER DEPOSITED SCALE FROM THE SURFACE OF AWATER CONTAINER WHICH INCLUDES THE STEPS OF REMOVING THE SCALE FROM THESURFACE BY PASSING HYDROGEN ZEOLITE WATER OVER THE SURFACE, THE WATERHAVING AN ACID PH AND CONTINUING THE TREATMENT UNTIL THE PH OF THE WATERAFTER PASSING OVER THE SURFACR REMAINS SUBSTANTIALLY CONSTANT AND UNTILTHE PH OF THE WATER